Re: [PATCH 05/14] iomap: Support THPs in invalidatepage

Darrick J. Wong
2020-10-14T16:35:55Z

On Wed, Oct 14, 2020 at 04:03:48AM +0100, Matthew Wilcox (Oracle) wrote:
> If we're punching a hole in a THP, we need to remove the per-page
> iomap data as the THP is about to be split and each page will need
> its own. This means that writepage can now come across a page with
> no iop allocated, so remove the assertion that there is already one,
> and just create one (with the uptodate bits set) if there isn't one.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> fs/iomap/buffered-io.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 95ac66731297..4633ebd03a3f 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -60,6 +60,8 @@ iomap_page_create(struct inode *inode, struct page *page)
> iop = kzalloc(struct_size(iop, uptodate, BITS_TO_LONGS(nr_blocks)),
> GFP_NOFS | __GFP_NOFAIL);
> spin_lock_init(&iop->uptodate_lock);
> + if (PageUptodate(page))
> + bitmap_fill(iop->uptodate, nr_blocks);
> attach_page_private(page, iop);
> return iop;
> }
> @@ -494,10 +496,14 @@ iomap_invalidatepage(struct page *page, unsigned int offset, unsigned int len)
> * If we are invalidating the entire page, clear the dirty state from it
> * and release it to avoid unnecessary buildup of the LRU.
> */
> - if (offset == 0 && len == PAGE_SIZE) {
> + if (offset == 0 && len == thp_size(page)) {
> WARN_ON_ONCE(PageWriteback(page));
> cancel_dirty_page(page);
> iomap_page_release(page);
> + } else if (PageTransHuge(page)) {
> + /* Punching a hole in a THP requires releasing the iop */
> + WARN_ON_ONCE(!PageUptodate(page) && PageDirty(page));
> + iomap_page_release(page);
> }
> }
> EXPORT_SYMBOL_GPL(iomap_invalidatepage);
> @@ -1363,14 +1369,13 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> struct writeback_control *wbc, struct inode *inode,
> struct page *page, u64 end_offset)
> {
> - struct iomap_page *iop = to_iomap_page(page);
> + struct iomap_page *iop = iomap_page_create(inode, page);
> struct iomap_ioend *ioend, *next;
> unsigned len = i_blocksize(inode);
> u64 file_offset; /* file offset of page */
> int error = 0, count = 0, i;
> LIST_HEAD(submit_list);
>
> - WARN_ON_ONCE(i_blocks_per_page(inode, page) > 1 && !iop);
> WARN_ON_ONCE(iop && atomic_read(&iop->write_bytes_pending) != 0);
>
> /*
> @@ -1415,7 +1420,6 @@ iomap_writepage_map(struct iomap_writepage_ctx *wpc,
> */
> if (wpc->ops->discard_page)
> wpc->ops->discard_page(page);
> - ClearPageUptodate(page);

Er, I don't get it -- why do we now leave the page up to date after
writeback fails?

--D

> unlock_page(page);
> goto done;
> }
> --
> 2.28.0
>